In response to increases in data transmission and data processing rates brought about by broadband communications and interactive telecommunication and computer services, there is a need for increased interconnection density and capacity in electronic equipment, and particularly in circuitized substrates which form part of such equipment. This need has led to a growing reliance upon optical means such as optical fibers as a replacement for traditional wire (e.g., copper) transmission lines. In some situations involving long distance transmissions, such a demand has resulted in the almost complete replacement of copper wire with optical fiber. The advantages of doing so include lower transmission losses and superior bandwidth characteristics. Optical transmission can also improve system performance if applied at short distances, for example, such as between physically adjacent equipment racks and cabinets, or between offices in a given building. However, the benefits of optical fiber transmission extend to even shorter distances, as at intra-board level among integrated circuits and other components on a single circuitized substrate (e.g., circuit board). This also applies at the intra-module level for interconnecting such components as very large scale (VLSI) and ultra large scale (ULSI) integrated circuits and chip subassemblies in a single electronic module. Use of such optical connections is also considered advantageous because such close (and more distant) transmissions are able to do so at gigabyte speeds.
Still further advantages of optical interconnections over electrical conductors at the substrate and module level include immunity to electromagnetic interference (EMI) or electrical noise, electrical isolation of interconnected components, far less frequency dependent signal degradation, and higher possible density of necessary interconnects due to lack of cross-talk between closely spaced, fine conductors.
Two examples of present efforts to provide optical interconnections at the circuitized substrate level are illustrated in the optical flex technology such as that marketed by Advanced Interconnection Technology, LLC of Islip, N.Y. and the optical flex foil approach which is part of the Apollo Demonstrator project at the Micro Interconnect Research Center of L M Ericsson, Stockholm, Sweden (described in Ericsson review, No. 2, 1995, vol. 72). In general, these optical interconnections involve arranging lengths of optical fibers in a desired pattern customized to the intended application, laminating the optical fibers between sheets of a flexible foil and applying appropriate connectors and terminations to the fiber ends. The lamination holds both the fibers and the connectors in the desired layout. The flex foil is then assembled to a conventional rigid circuit board simply by plugging the connectors to corresponding mating connectors on the circuit board. Mechanical supports may be provided on the circuit board for stabilizing the flex foil in place rather than relying on the fiber connectors alone for this purpose. The flex foil is typically supported in spaced relationship above the electrical components on the board. It has also been suggested that the flex foil be laminated or bonded to a rigid circuit board to thereby integrate optical and electrical interconnects.
It is understood that the above two examples and those represented in the patents listed below are not an exhaustive summary of those possibly available in the field. Further, the citation of these documents is not an admission that any is prior art to the present invention.
In U.S. Pat. No. 6,996,305, there is described a printed circuit board (hereinafter also referred to simply as a PCB) with opto-via holes for transmitting an optical signal to an optical waveguide in the PCB, and a process of forming the opto-via holes. The process comprises forming a plurality of via holes on a plurality of copper-clad laminates using a drill, plating an inner wall of each via hole, exposing and etching the plated portions of an upper and lower side of each copper clad laminate to form a circuit pattern on the upper and lower side of the copper clad laminate, layering the patterned copper clad laminates on each other using an insulating resin adhesive, and removing the insulating resin adhesive in the predetermined via holes to form opto-via holes. According to the authors, the process is advantageous because the optical signal is stably transmitted to the optical waveguide in the PCB without damaging the optical waveguide directly exposed to an external environment, and the optical waveguide suitable to physical properties of the material constituting the PCB is easily inserted between the inner layer and the outer layer.
In U.S. Pat. No. 7,045,897, there is described an electrical assembly which includes a circuitized substrate comprised of an organic dielectric material having a first electrically conductive pattern thereon. At least part of the dielectric layer and pattern form the first, base portion of an organic memory device, the remaining portion being a second, polymer layer formed over the part of the pattern and a second conductive circuit formed on the polymer layer. A second dielectric layer if formed over the second conductive circuit and first circuit pattern to enclose the organic memory device. The device is electrically coupled to a first electrical component through the second dielectric layer and this first electrical component is electrically coupled to a second electrical component. A method of making the electrical assembly is also provided, as is an information handling system adapted for using one or more such electrical assemblies as part thereof. U.S. Pat. No. 7,045,897 is assigned to the same Assignee as the present invention.
In U.S. Pat. No. 7,136,551, there is described an optical printed circuit board (PCB) having a multi-channel optical waveguide, which comprises an optical waveguide having an optical path for transmitting light beams, a groove for penetrating the optical waveguide and an optical interconnection block inserted in the groove and connected to the optical waveguide to transmit the light beams, wherein the optical interconnection block includes an optical fiber bundle bent by the angle of 90 degrees. The optical interconnection block connects a plurality of multi-layered optical waveguides to transmit light beams to the optical waveguides. The optical fiber bundle is installed as a medium of the multi-channel optical waveguide in the optical PCB.
In U.S. Pat. No. 7,149,376, there is described a circuit board with embedded optical fibers terminating in fiber ends which face into holes defined in the circuit board and optoelectronic emitter or detector modules mounted in the holes in optical coupling with the fiber ends. Each module is electrically connected to circuit traces on the circuit board and is optically coupled to one or more optical fibers terminating on a side surface of the hole. The modules have an optical axis oriented into the hole and a reflector supported in the hole for optically coupling the photo emitter/detector module with the fiber ends on the side surface of the hole.
In U.S. Pat. No. 7,149,389, there is described an optical printed circuit board system having a tapered optical waveguide. The system includes a substrate as a printed circuit board having an electrical circuit and on which an electrical circuit chip is mounted, a system board including an optical bench coupled to the substrate and on which a photoelectrical signal chip electrically connected to the electrical circuit chip through the electrical circuit, an optical device electrically connected to the photoelectrical signal chip, and a first optical waveguide aligned to the optical device for optical coupling. The waveguide is tapered to have a smaller aperture in an output node for outputting the optical signals smaller than that in an input node for inputting the optical signals. The system further includes a back plane including a groove into which the system board is inserted and a second optical waveguide optically coupled to the first optical waveguide and tapered to have a smaller aperture in the output node than in the input node. The input node of the first optical waveguide is optically coupled to the output node of the second optical waveguide or the output node of the first optical waveguide is optically coupled to the input node of the second optical waveguide.
In U.S. Pat. No. 7,212,713, there is described an optical transmission substrate including: a first substrate; an optical waveguide which has clad covering a core and a periphery of the core and extends on an upper surface of the first substrate; a second substrate provided parallel to the first substrate so that a lower surface thereof contacts an upper surface of the optical waveguide; a reflection surface which is provided on a cross section of the core at an end of the optical waveguide and reflects light, which travels through the core of the optical waveguide, toward the second substrate; and a light guide which is provided in the second substrate and guides the light, which is reflected toward the second substrate, toward an upper surface of the second substrate from a position closer to the core than an upper surface of the clad.
In U.S. Pat. No. 7,223,023, there are described optoelectronic transmission and/or reception arrangements having a surface-mounted optoelectronic component and a circuit board provided with electrical lines, the optoelectronic component being surface-mounted on the circuit board, the optical axis of the optoelectronic component running perpendicular to the plane of the circuit board. In one embodiment, provision is made of a holding apparatus for receiving and orienting an optical waveguide to be coupled to the optoelectronic component, which holding apparatus directly adjoins the side of the optoelectronic component that is remote from the circuit board. In another embodiment, the circuit board has a cutout and light is coupled into or out of the optoelectronic component in the direction of the cutout of the circuit board.
In U.S. Pat. No. 7,224,857, there is described an optical-routing board for an opto-electrical system having optical waveguides embedded in non-laminated optical substrates that enable optical signals to be routed among opto-electric components mounted on the top surfaces of the optical substrates. Methods for making the optical-routing boards are also disclosed. The waveguides are formed by focused pulse-laser writing, with the focal point of the pulsed-laser beam being moved in a three-dimensional manner through the non-laminated substrate. Bevel surfaces are preferably formed in the substrate to facilitate bending of the waveguides.
In U.S. Pat. No. 7,228,020, there is described an optoelectronic arrangement having a surface-mountable semiconductor module having at least one optoelectronic transmitting and/or receiving unit, a housing, in which the optoelectronic transmitting and/or receiving unit is arranged, and a mounting side of the housing, which, in the case of surface mounting of the semiconductor module on a printed circuit board, faces the printed circuit board. The arrangement furthermore has a cooling element, which is thermally coupled to the semiconductor module for the purpose of cooling the optoelectronic transmitting and/or receiving unit. The cooling element is arranged on a side of the housing that is remote from the mounting side.
In U.S. Publication 2006/0210213, there is described an optical backplane providing integrated optical couplers for coupling to external optical fibers, along with a method for making the same. One optical backplane has a first cladding layer disposed over the top surface of a substrate, and at least a first core body disposed over the first cladding layer, with the first core body having a first end and a second end. A material layer is disposed above the first cladding layer and the first end of the first core body, with the material layer having a top surface and a bottom surface. A focusing element is formed at the top surface of the material layer, with the focusing element being located above the first end of the first core body.
In Japanese Patent Application Publication No. 2000-121859, there is described a method of manufacturing an embedded type optical waveguide device. This method involves manufacturing an optical waveguide device by (1) depositing an “undercladding” layer over a silica glass substrate, (2) forming a mask over the undercladding layer, (3) using this mask to form a groove for accommodating a core, (4) depositing a core layer over the undercladding layer, (5) forming a core by leaving the core layer inside the groove and removing other portion of the core layer on the undercladding layer by chemical-mechanical polishing, and (6) forming an “overcladding” layer over the core and the undercladding layer.
In U.S. Pat. No. 6,690,845 issued to Yoshimura et al., there is disclosed three-dimensional opto-electronic modules having a plurality of opto-electronic (O/E) layers, with optical signals being routed between O/E layers within one or more three-dimensional volumes. The O/E layers are disposed over and above one another with at least one of their edges aligned to one another. At least two of the O/E layers have waveguides with ends near the aligned edges. A plurality of Z-connector arrays are disposed between the O/E layers and within the three-dimensional volumes to provide a plurality of Z-direction waveguides. A first vertical optical coupler couples light from one waveguide in one O/E layer to a Z-direction waveguide, and a second vertical optical coupler couples the light from the Z-direction waveguide to a second waveguide in a second O/E layer.
As defined herein, the present invention defines the formation of a circuitized substrate during which at least one (and possibly several) optical pathways are formed which are capable of having optical signals pass there-through and eventually exit the substrate, e.g., to be coupled to an external optoelectronic component such as a transmitter-receiver device. The method used to accomplish this formation utilizes many conventional processes used in producing printed circuit boards and is thus able to provide an effective and cost-reduced process compared to processes such as those described above. It is believed that such a method would constitute a significant advancement in the art.